Although electric vehicles are used as a counter measurement of the automobile exhaust for reducing the air contamination, the electric vehicles have not been prevailed because of the drawbacks such as lack of battery charging facilities and insufficient mileage per charge. Thus, a vehicle applied with a fuel cell is considered to be the most environmentally benign automobile of great promise. Among the fuel cells, a solid polymer electrolyte fuel cell is the most capable fuel cell for the automobile because the fuel cell is operated under the low temperature.
Generally, plural single cells are stacked to form a fuel cell. The single cell includes an electrolyte sandwiched by two electrodes (i.e., a fuel electrode and an oxidant electrode) and separators which sandwich the electrodes. A fuel gas and an oxidant gas are supplied to the fuel electrode and the oxidant electrode respectively via gas passages provided on respective separators for generating the electric power by the electrochemical reaction. Thus, the fuel cell is recognized as an environmentally benign power generation device without exhaust except the water.
The solid polymer electrolyte fuel cell includes a polymer ion exchange membrane (i.e., solid polymer electrolyte membrane) as an electrolyte. The fuel gas including the humidified hydrogen or the hydrogen reaches a catalyst layer via a gas diffusion layer of the fuel electrode which also serves as a current collector to cause the following reaction.2H2→4H++4e−  (1)
A proton H+ generated at the fuel electrode moves towards the oxidant electrode via the electrolyte accompanied with the water molecule. Simultaneously, the electron e− generated at the fuel electrode is moved towards the oxidant electrode through the gas diffusion layer and the catalyst layer (i.e., current collector) and through a resistance connected between the fuel electrode and the oxidant electrode via an external circuit.
On the other hand, at the oxidant electrode, the oxidant gas including the humidified oxygen reaches the catalyst layer through the gas diffusion layer of the oxidant electrode which is also the current collector. The oxygen receives the electron flowed from the external circuit via the gas diffusion layer (i.e., current collector) and via the catalyst layer to be deoxidized following the following reaction. Then oxygen is bonded to the proton H+ moved from the fuel electrode via the electrolyte membrane to become the water.4H++4e−+O2→2H2O  (2)
A part of the generated water is entered into the electrolyte membrane due to the higher concentration gradient of the electrolyte membrane, and is diffused to be moved towards the fuel electrode. A part of the generated water is evaporated to be diffused to the gas passage via the catalyst layer and the gas diffusion layer to be exhausted along with the non-reacting oxidant gas. Thus, when the gas diffusion layer of the fuel electrode and the oxidant electrode do not have sufficient water repellency, the water vapor is apt to be condensed to become the water, which may be the obstruction for the transportation of the reactant and the product.
Gas diffusion layers of the fuel electrode side and the oxidant electrode side construct an electric circuit by contacting convex portions of the respective separators. Thus, it is required to reduce the contact resistance between the gas diffusion layers and the separator to the minimum. Further, because the separator is generally made of metal or carbon which do not have high water repellency, the water is condensed at the contact portion to cause the flooding phenomenon to deteriorate the power generation performance unless the water repellency of the contact portion between the gas diffusion layer and the separator is high.
A known fuel cell electrode and the manufacturing method thereof is disclosed in Japanese Patent Laid-Open Publication No. H08-185867. In this known fuel cell electrode, a highly porous carbon paper with electric conduction is impregnated with the tetrafluoroethylene (i.e., hereinafter referred as PTFE) dispersion and is sintered to become a substrate having water repellency. A catalyst layer is formed on one side of the substrate.
Notwithstanding, in the known fuel cell electrode and the manufacturing method thereof disclosed in Japanese Patent Laid-Open publication No. H08-185867, because the gas diffusion layer includes the structure in which the water repellent and the insulating PTFE particles are dispersedly attached to the substrate serving as the current collector, the contact resistance between the gas diffusion layer and the separator is large. In addition, because the water repellency of the contact portion between the gas diffusion layer and the separator is insufficient, the power generation performance is insufficient and the condensation of the water at the contact portion cannot be eradicated.
A need thus exists for a manufacturing method of a fuel cell electrode which includes small contact resistance with a separator and which is hard to cause the flooding phenomenon at a contact portion with the separator, and for a fuel cell with high power generation performance and high reliability.